They must have been inside the school for some time judging by the amount of damage, he said.
They took paint from a teacher's storage locker and spread it over the hallways in the building, on walls, ceilings, doors and windows, Stapleford said. They did not enter any classrooms.
Carpeting throughout the building was ruined by the paint.
At one place, janitors had put a floor fan in an area of the corridor where they had just shampooed the carpeting. The fan was there to dry the carpet.
The vandals put paint near the fan and turned it on. The result was paint sprayed over a wide area, Stapleford said.
A private contractor was hired to clean up the mess, he said. Many walls have to be repainted and a lot of ceiling tiles have to be replaced.
New carpeting has to be replaced in all hallways, a job that is expected to be completed over the weekend in time for the start of school Monday, he said.
Teachers and staff members returned to school Monday, he said.
Stapleford said he expects the damage to be covered by insurance.
He said charges will be pressed against those involved.
"I've been in education for 18 years and I've never seen anything like this before," Stapleford said. "There is no sense to it. It really, truly is a shame. It's pretty bad."
A Mercersburg Police Department patrolman declined to comment on the case Tuesday. He referred questions to Mercersburg Police Chief Larry Thomas, who was unavailable and did not immediately return a phone call Tuesday afternoon.